CHW-4101 SignupValidation

signup payload failed validation; email, password, and org_name are required

Default message: signup payload failed validation; email, password, and org_name are required
HTTP status: 400 (client)

Problem. A signup, password reset, or TOTP-related field failed shape validation before any business logic ran. Cause. Missing email, password, or org_name; unknown plan_id; empty org slug; missing TOTP code; etc. Fix. Consult the endpoint documentation and resubmit with the required fields populated. HTTP 400.